Field of the Invention
The present invention relates generally to a method and connector device to provide a good electrical and hydraulic connection for a water-cooled conductor, and more specifically, the present invention relates to a method and connector device for providing a good electrical and hydraulic connection for turbogenerator stator bars formed from a plurality of hollow water-cooled conductors.
Description of the Prior Art
In large turbogenerators, excessive heating can occur due to the very large currents that are involved. Accordingly, hollow conductors are utilized so that water may be passed therethrough to remove the undesired heat. Although different shapes may be employed, the most common assembly of water-cooled conductors involves a pair of rows of generally rectangular conductors formed into a generally rectangular conductor bar. These conductor bars are then employed as the windings for the extremely large turbogenerators.
Cooling water for the hollow conductors is normally introduced at the end turn area of the turbogenerator windings. A conventional practice is to utilize a connector to which the end of a conductor bar is brazed, with provision for inserting water into the open end of the hollow conductors. The end turns are completed by electrically connecting appropriate connectors.
One type of connector is essentially in the form of a hollow box. The conductor bar is inserted partially into the connector box and brazed to the box. Water is then inserted into the other end of the box to be passed through the open end of the hollow conductors. In order to make such an arrangement work, the brazing of the conductor bar to the box should be such as to provide a strong mechanical joint, a continuous electrically conductive path, and a water-tight seal. While prior art approaches have frequently been able to provide the strong mechanical joint, the electrical, and especially the hydraulic, aspects of these brazed joints have frequently been deficient.
Prior art brazed joints have conventionally been achieved by feeding the brazing material along the conductors toward the open ends of the hollow conductors. Such an approach relies upon the capillary action of the brazing material. Dependence upon the capillary action results in a number of problems. First of all, in order to keep the brazing material moving along the conductors, it is necessary to utilize relatively high temperatures to achieve brazing material flow along even the relatively limited length which may be achieved. In addition, the brazing material tends to flow to the smaller gaps or spaces, and hence it is difficult to get enough brazing material in the relatively larger spaces, such as at the rounded corners of the conductors. Still further, in order to achieve the desired electrical and hydraulic characteristics, both the box and the conductor bar must be constructed to fairly tight tolerances (a total tolerance in the order of .001 or .002 inch is required), which is extremely difficult to achieve with a conductor bar. Therefore, many prior art braze joints exhibit poor electrical characteristics and a tendency toward porosity with respect to the cooling water. Inasmuch as the failure of a large turbogenerator can result in the loss of many tens of thousands of dollars worth of electrical power each day that the turbogenerator is not operating, the failure of a brazed joint is very serious.